Portable Network Graphics - Revision history

Mdejong: Add mention of AVAnimator library for iPhone devs.

2011-05-24T20:21:22Z

Add mention of AVAnimator library for iPhone devs.

← Older revision		Revision as of 13:21, 24 May 2011
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	===Animation===		===Animation===
	PNG does not offer animation. [[Multiple-image Network Graphics\|MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. APNG is now supported in firefox trunk so will likely see wider use.		PNG does not offer animation. [[Multiple-image Network Graphics\|MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. APNG is now supported in firefox trunk so will likely see wider use. For iPhone/iPad developers, the AVAnimator library is available to add APNG support.

	[http://wiki.mozilla.org/APNG_Specification APNG Specification]		[http://wiki.mozilla.org/APNG_Specification APNG Specification]
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	[https://bugzilla.mozilla.org/show_bug.cgi?id=257197 Discussion about APNG implementation in firefox]		[https://bugzilla.mozilla.org/show_bug.cgi?id=257197 Discussion about APNG implementation in firefox]

			[http://www.modejong.com/AVAnimator/ AVAnimator]

	[[Category:Image Formats]]		[[Category:Image Formats]]

AConverse: /* Compression */

2009-02-17T16:55:34Z

Compression

← Older revision		Revision as of 09:55, 17 February 2009
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	===Compression===		===Compression===
	PNG uses a non-patented lossless data compression ~~method~~ known as ~~deflation~~. This method is combined with prediction, where for each image line, a ''filter method'' is chosen that predicts the color of each pixel based on the colors of previous pixels and subtracts the predicted color of the pixel from the actual color. An image line filtered in this way is often more compressible than the raw image line would be, especially if it is similar to the line above (since ~~deflate~~ has no understanding that an image is a 2D entity, and instead just sees the image data as a stream of bytes).		PNG uses a non-patented lossless data compression algorithm known as [[DEFLATE]]. This method is combined with prediction, where for each image line, a ''filter method'' is chosen that predicts the color of each pixel based on the colors of previous pixels and subtracts the predicted color of the pixel from the actual color. An image line filtered in this way is often more compressible than the raw image line would be, especially if it is similar to the line above (since DEFLATE has no understanding that an image is a 2D entity, and instead just sees the image data as a stream of bytes).

	===Interlacing===		===Interlacing===

Crybaby: /* Animation */ add link to apng samples

2007-12-17T03:21:15Z

Animation: add link to apng samples

← Older revision		Revision as of 20:21, 16 December 2007
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	PNG does not offer animation. [[Multiple-image Network Graphics\|MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. APNG is now supported in firefox trunk so will likely see wider use.		PNG does not offer animation. [[Multiple-image Network Graphics\|MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. APNG is now supported in firefox trunk so will likely see wider use.

	[http://wiki.mozilla.org/APNG_Specification APNG Specification]		[http://wiki.mozilla.org/APNG_Specification APNG Specification]

			[http://people.mozilla.com/~dolske/apng/demo.html APNG Samples (with GIF animations for comparison)]

	[https://bugzilla.mozilla.org/show_bug.cgi?id=257197 Discussion about APNG implementation in firefox]		[https://bugzilla.mozilla.org/show_bug.cgi?id=257197 Discussion about APNG implementation in firefox]

	[[Category:Image Formats]]		[[Category:Image Formats]]

Multimedia Mike: /* Animation */ expand MNG wiki link

2007-10-30T21:30:34Z

Animation: expand MNG wiki link

← Older revision		Revision as of 14:30, 30 October 2007
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	===Animation===		===Animation===
	PNG does not offer animation. [[MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. APNG is now supported in firefox trunk so will likely see wider use.		PNG does not offer animation. [[Multiple-image Network Graphics\|MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. APNG is now supported in firefox trunk so will likely see wider use.

	[http://wiki.mozilla.org/APNG_Specification APNG Specification]		[http://wiki.mozilla.org/APNG_Specification APNG Specification]

Multimedia Mike: PNG moved to Portable Network Graphics: proper expanded name

2007-10-30T21:22:01Z

PNG moved to Portable Network Graphics: proper expanded name

← Older revision	Revision as of 14:22, 30 October 2007
(No difference)

Multimedia Mike: start filling in MIME types for container formats

2007-10-30T20:56:16Z

start filling in MIME types for container formats

← Older revision		Revision as of 13:56, 30 October 2007
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			* Extension: PNG
			* MIME Types:
			** png: image/png or image/x-png

	===File header===		===File header===
	A PNG file starts with an 8-byte signature. The hexadecimal byte values are 89 50 4E 47 0D 0A 1A 0A. Each of the header bytes is there for a specific reason [http://www.libpng.org/pub/png/spec/1.1/PNG-Rationale.html#R.PNG-file-signature]:		A PNG file starts with an 8-byte signature. The hexadecimal byte values are 89 50 4E 47 0D 0A 1A 0A. Each of the header bytes is there for a specific reason [http://www.libpng.org/pub/png/spec/1.1/PNG-Rationale.html#R.PNG-file-signature]:

Crybaby: add Animation chunks

2007-07-18T01:25:25Z

add Animation chunks

← Older revision		Revision as of 18:25, 17 July 2007
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	The lowercase first letter in these chunks indicates that they are not needed for the PNG specification. The lowercase last letter in some chunks indicates that they are safe to copy, even if the application concerned does not understand them.		The lowercase first letter in these chunks indicates that they are not needed for the PNG specification. The lowercase last letter in some chunks indicates that they are safe to copy, even if the application concerned does not understand them.

			====Animation chunks====
			Animation control chunks must appear before the IDAT chunk. If they appear after the IDAT chunk they should be ignored (according to the spec)

			Control Chunks:
			* aCTL (Animation Control Chunk)
			offset 0: unsigned 32bits: Number of times to loop this APNG. 0 indicates infinite looping.
			* fCTL (Frame Control Chunk)

			offset: 0: unsigned 32bits: X position at which to render this frame
			offset: 4: unsigned 32bits: Y position at which to render this frame
			offset: 8: unsigned 16bits: Frame delay fraction numerator
			offset: 10: unsigned 16bits: Frame delay fraction denominator
			offset: 12: byte (signed/unsigned?) Type of canvas area disposal to be done after rendering this frame

			Data Chunks:
			* aDAT (Animation Data Chunk)
			offset: 0: unsigned 32bits: Sequence number of this aDAT chunk, starting with 0
			offset: 4: remaining stream data

			Chunks that are re-appropriated.
			* PLTE (Palette Chunk)
			* tRNS (Transparency Chunk)

			These chunks are treated as Global Palette and Global Transparency.
			The palette and transparency can be changed for any frame by adding a PLTE or tRNS chunk between the frame's IHDR and IDAT chunks.

	===Colour depth===		===Colour depth===

Crybaby: /* Animation */ add more info about APNG

2007-07-17T05:12:36Z

Animation: add more info about APNG

← Older revision		Revision as of 22:12, 16 July 2007
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	===Animation===		===Animation===
	PNG does not offer animation. [[MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. ~~However neither of these formats are widely~~ supported.		PNG does not offer animation. [[MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. APNG is now supported in firefox trunk so will likely see wider use.

			[http://wiki.mozilla.org/APNG_Specification APNG Specification]

			[https://bugzilla.mozilla.org/show_bug.cgi?id=257197 Discussion about APNG implementation in firefox]

	[[Category:Image Formats]]		[[Category:Image Formats]]

Crybaby: /* Animation */

2007-04-20T04:39:06Z

Animation

← Older revision		Revision as of 21:39, 19 April 2007
Line 132:		Line 132:

	===Animation===		===Animation===
	PNG does not offer animation. MNG is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. However neither of these formats are widely supported.		PNG does not offer animation. [[MNG]] is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. However neither of these formats are widely supported.

	[[Category:Image Formats]]		[[Category:Image Formats]]

DonDiego: Remove non-existing templates, add a few newlines.

2006-10-22T12:24:14Z

Remove non-existing templates, add a few newlines.

← Older revision		Revision as of 05:24, 22 October 2006
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	\|A unix newline (LF) to detect UNIX-DOS line ending conversion.		\|A unix newline (LF) to detect UNIX-DOS line ending conversion.
	\|}		\|}

	==="Chunks" within the file===		==="Chunks" within the file===
	After the header come a series of chunks each of which conveys certain information about the image. Chunks declare themselves as ''critical'' or ''ancillary'', and a program encountering an ancillary chunk that it does not understand can safely ignore it. This chunk-based structure is designed to allow the PNG format to be extended while maintaining compatibility with older versions.		After the header come a series of chunks each of which conveys certain information about the image. Chunks declare themselves as ''critical'' or ''ancillary'', and a program encountering an ancillary chunk that it does not understand can safely ignore it. This chunk-based structure is designed to allow the PNG format to be extended while maintaining compatibility with older versions.
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	The case of the fourth letter indicates if a chunk is safe to copy by editors that do not recognise it. If lowercase the chunk may be safely copied regardless of the extent of modifications to the file. If uppercase it may only be copied if the modifications have not touched any critical chunks.		The case of the fourth letter indicates if a chunk is safe to copy by editors that do not recognise it. If lowercase the chunk may be safely copied regardless of the extent of modifications to the file. If uppercase it may only be copied if the modifications have not touched any critical chunks.

	====Essential chunks====		====Essential chunks====
	A decoder must be able to interpret these to read and render a PNG file.		A decoder must be able to interpret these to read and render a PNG file.
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	The lowercase first letter in these chunks indicates that they are not needed for the PNG specification. The lowercase last letter in some chunks indicates that they are safe to copy, even if the application concerned does not understand them.		The lowercase first letter in these chunks indicates that they are not needed for the PNG specification. The lowercase last letter in some chunks indicates that they are safe to copy, even if the application concerned does not understand them.

	===Colour depth===		===Colour depth===
	PNG images can either use palette-indexed color or be made up of one or more channels (numerical values directly representing quantities about the pixels). When there is more than one channel in an image all channels have the same number of bits allocated per pixel (known as the bitdepth of the channel). Although the PNG specification always talks about the bitdepth of channels, most software and users generally talk about the total number of bits per pixel (sometimes also referred to as bitdepth or color depth).		PNG images can either use palette-indexed color or be made up of one or more channels (numerical values directly representing quantities about the pixels). When there is more than one channel in an image all channels have the same number of bits allocated per pixel (known as the bitdepth of the channel). Although the PNG specification always talks about the bitdepth of channels, most software and users generally talk about the total number of bits per pixel (sometimes also referred to as bitdepth or color depth).
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	\|-		\|-
	\|indexed (color type 3)		\|indexed (color type 3)
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|{{no}}		\|no
	\|-		\|-
	\|greyscale (color type 0)		\|greyscale (color type 0)
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|-		\|-
	\|greyscale & alpha<br />(color type 4)		\|greyscale & alpha<br />(color type 4)
	\|{{no}}		\|no
	\|{{no}}		\|no
	\|{{no}}		\|no
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|-		\|-
	\|truecolor<br />(RGB - color type 2)		\|truecolor<br />(RGB - color type 2)
	\|{{no}}		\|no
	\|{{no}}		\|no
	\|{{no}}		\|no
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|-		\|-
	\|truecolor & alpha<br />(RGBA - color type 6)		\|truecolor & alpha<br />(RGBA - color type 6)
	\|{{no}}		\|no
	\|{{no}}		\|no
	\|{{no}}		\|no
	\|{{yes}}		\|yes
	\|{{yes}}		\|yes
	\|}		\|}

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	Indexed color PNGs are allowed to have 1, 2, 4 or 8 bits per pixel by the standard; greyscale images with no alpha channel allow for 1, 2, 4, 8 or 16 bits per pixel. Everything else uses a bitdepth per channel of either 8 or 16. The combinations this allows are given in the table above. The standard requires that decoders can read all supported color formats but many image editors can only produce a small subset of them.		Indexed color PNGs are allowed to have 1, 2, 4 or 8 bits per pixel by the standard; greyscale images with no alpha channel allow for 1, 2, 4, 8 or 16 bits per pixel. Everything else uses a bitdepth per channel of either 8 or 16. The combinations this allows are given in the table above. The standard requires that decoders can read all supported color formats but many image editors can only produce a small subset of them.

	===Transparency of image===		===Transparency of image===
	PNG offers a variety of transparency options. With truecolor and greyscale images either a single pixel value can be declared as transparent or an alpha channel can be added. For paletted images, alpha values can be added to palette entries. The number of such values stored may be less than the total number of palette entries, in which case the remaining entries are considered fully opaque.		PNG offers a variety of transparency options. With truecolor and greyscale images either a single pixel value can be declared as transparent or an alpha channel can be added. For paletted images, alpha values can be added to palette entries. The number of such values stored may be less than the total number of palette entries, in which case the remaining entries are considered fully opaque.

	The scanning of pixel values for binary transparency is supposed to be performed before any color reduction to avoid pixels becoming unintentionally transparent. This is most likely to pose an issue for systems that can decode 16 bits per channel images (as they must to be compliant with the specification) but only output at 8 bits per channel (the norm for all but the highest end systems).		The scanning of pixel values for binary transparency is supposed to be performed before any color reduction to avoid pixels becoming unintentionally transparent. This is most likely to pose an issue for systems that can decode 16 bits per channel images (as they must to be compliant with the specification) but only output at 8 bits per channel (the norm for all but the highest end systems).

	===Compression===		===Compression===
	PNG uses a non-patented lossless data compression method known as deflation. This method is combined with prediction, where for each image line, a ''filter method'' is chosen that predicts the color of each pixel based on the colors of previous pixels and subtracts the predicted color of the pixel from the actual color. An image line filtered in this way is often more compressible than the raw image line would be, especially if it is similar to the line above (since deflate has no understanding that an image is a 2D entity, and instead just sees the image data as a stream of bytes).		PNG uses a non-patented lossless data compression method known as deflation. This method is combined with prediction, where for each image line, a ''filter method'' is chosen that predicts the color of each pixel based on the colors of previous pixels and subtracts the predicted color of the pixel from the actual color. An image line filtered in this way is often more compressible than the raw image line would be, especially if it is similar to the line above (since deflate has no understanding that an image is a 2D entity, and instead just sees the image data as a stream of bytes).

	===Interlacing===		===Interlacing===
	PNG offers an optional 2-dimensional, 7-pass interlacing scheme – the Adam7 algorithm. This is more sophisticated than GIF's 1-dimensional, 4-pass scheme, and allows a clearer low-resolution image to be visible earlier in the transfer. However, as a 7-pass scheme, it tends to reduce the data's compressibility more than simpler schemes.		PNG offers an optional 2-dimensional, 7-pass interlacing scheme – the Adam7 algorithm. This is more sophisticated than GIF's 1-dimensional, 4-pass scheme, and allows a clearer low-resolution image to be visible earlier in the transfer. However, as a 7-pass scheme, it tends to reduce the data's compressibility more than simpler schemes.

	===Animation===		===Animation===
	PNG does not offer animation. MNG is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. However neither of these formats are widely supported.		PNG does not offer animation. MNG is an image format that supports animation and is based on the ideas and some of the chunks of PNG but is a complex system and does not offer fallback to single image display like GIF does. APNG is another image format based on PNG that supports animation and is simpler than MNG. APNG offers fallback to single image display for PNG decoders that do not support APNG. However neither of these formats are widely supported.

	[[Category:Image Formats]]		[[Category:Image Formats]]